Plastics have now widely penetrated into daily life and every field of industry; the global yearly production of plastics has reached about one hundred million tons. Most parts of the plastics are discarded after use, which has been recognized as a cause to disturb the global environment. Accordingly, materials that give no adverse effects on the global environment even after they are discarded are demanded.
Further, petroleum and the like, which are raw materials for ordinary plastics, are exhaustive resources and therefore utilization of renewable resources is demanded. For example, plastics derived from plant raw materials can be obtained from renewable and non-exhaustive resources, so that the exhaustive resources such as petroleum can be saved, and in addition, after their use, they are biodegraded and naturalized, thus having excellent recyclability.
Among the plastics derived from plant materials, lactic acid based resins can be mass-produced by chemical engineering from lactic acid obtained by fermentation of starch as a raw material and are excellent in transparence, rigidity, heat resistance and so on. Therefore, in particular, the lactic acid based resins have attracted much attention as a substitute material for polystyrene and polyethylene terephthalate in the fields of injection molded articles such as film packaging materials, white goods, OA appliances, and automobile parts.
Injection molded articles for use in white goods, OA appliances, automobile parts and so on must have heat resistance to prevent fire. However, the lactic acid based resins have low glass transition temperatures and have poorer heat resistance than ABS resins, filler-contained polypropylene resins and the like. Therefore, the conventional lactic acid based resins have been difficult to use for white goods, OA appliances, and automobile parts.
Composite materials composed of a biodegradable resin and a natural fiber to improve the heat resistance of biodegradable resins is known. For example, Japanese Patent Application Laid-open Publication No. H09-169897 discloses a biodegradable fiber-reinforced molded article in which, for example, a natural fiber is bound to an aliphatic polyester resin in a dispersed state. Japanese Patent Application Laid-open Publication No. 2002-146219 discloses production of a biodegradable composite material by mixing a natural fiber and fine particulate biodegradable resin and hot press molding the resultant mixture.
However, these composite materials have insufficient heat resistance and may sometime cause a problem in their practical use.
Patent Document 1: Japanese Patent Application Laid-open Publication No. H09-169897
Patent Document 2: Japanese Patent Application Laid-open Publication No. 2002-146219